1. Field of the Invention
The present invention relates to an amplifier circuit used for an input stage of a comparator and the like.
2. Description of the Related Art
A fully differential operational amplifier having two input terminals and two output terminals is used for an input stage of a comparator and other various circuits. Compared with a single-ended operational amplifier, the fully differential operational amplifier is more tolerant of noise such as clock feedthrough. In order to make an average value of two-line output voltages constant, a common-mode feedback (CMFB) circuit is often added to the fully differential operational amplifier.
However, if the CMFB circuit is used, delay due to a feedback loop must be taken into consideration. For this reason, when the operational amplifier is used particularly in an open loop, the delay is one of factors that hinders the faster operation.